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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Intel XScale
®
Processor
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
120
Order Number: 306262-004US
When a memory access triggers a data breakpoint, the breakpoint is reported after the
access is issued. The memory access will not be aborted by the processor. The actual
timing of when the access completes with respect to the start of the debug handler
depends on the memory configuration.
On a data breakpoint, the processor generates a debug exception and re-directs
execution to the debug handler before the next instruction executes. The processor
reports the data breakpoint by setting the DCSR.MOE to 0b010. The link register of a
data breakpoint is always PC (of the next instruction to execute) + 4, regardless of
whether the processor is configured for monitor mode or halt mode.
3.6.7
Software Breakpoints
Mnemonics:
BKPT (See ARM* Architecture Reference Manual, ARMv5T)
Operation:
If DCSR[31] = 0, BKPT is a nop;
If DCSR[31] =1, BKPT causes a debug exception
The processor handles the software breakpoint as described in
.
3.6.8
Transmit/Receive Control Register
Communications between the debug handler and debugger are controlled through
handshaking bits that ensures the debugger and debug handler make synchronized
accesses to TX and RX. The debugger side of the handshaking is accessed through the
DBGTX (
“DBGTX JTAG Register” on page 127
) and DBGRX (
) JTAG Data Registers, depending on the direction of the data transfer.The
debug handler uses separate handshaking bits in TXRXCTRL register for accessing TX
and RX.
The TXRXCTRL register also contains two other bits that support high-speed download.
One bit indicates an overflow condition that occurs when the debugger attempts to
write the RX register before the debug handler has read the previous data written to
RX. The other bit is used by the debug handler as a branch flag during high-speed
download.
All of the bits in the TXRXCTRL register are placed such that they can be read directly
into the CC flags in the CPSR with an MRC (with Rd = PC). The subsequent instruction
can then conditionally execute based on the updated CC value